The present invention relates generally to the fields of data communications and modulator/demodulators (modems), and, more particularly, to a data communications system in which a plurality of modulation methods are used to facilitate communication among a plurality of modem types.
In existing data communications systems, a transmitter and receiver modem pair can successfully communicate only when the modems are compatible at the physical layer. That is, the modems must use compatible modulation methods. This requirement is generally true regardless of the network topology. For example, point-to-point, dial-up modems operate in either the industry standard V.34 mode or the industry standard V.22 mode. Similarly, in a multipoint architecture, all modems operate, for example, in the industry standard V.27bis mode. While the modems may be capable of using several different modulation methods, a single common modulation is negotiated at the beginning of a data session to be used throughout the duration of the session. Should it become necessary to change modulation methods, the existing data session is torn down, and a new session is negotiated using the new modulation method. Clearly, tearing down an existing data session causes a significant disruption in communication between the two modems.
As discussed in the foregoing, communication between modems is generally unsuccessful unless a common modulation method is used. In a point-to-point network architecture, if a modem attempts to establish a communication session with an incompatible modem, one or both of the modems will make several attempts to establish the communication link until giving up after a timeout period has expired or the maximum number of retry attempts has been reached. Essentially, communication on the link is impossible without replacing one of the modems such that the resulting modem pair uses a common modulation method.
In a multipoint architecture, a single central, or xe2x80x9cmaster,xe2x80x9d modem communicates with two or more tributary or xe2x80x9ctribxe2x80x9d modems using a single modulation method. If one or more of the trib modems are not compatible with the modulation method used by the master, those tribs will be unable to receive communications from the master. Moreover, repeated attempts by the master to communicate with the incompatible trib(s) will disturb communications with compatible trib(s) due to time wasted in making the futile communication attempts.
Thus, communication systems comprised of both high performance and low or moderate performance applications can be very cost inefficient to construct. For example, some applications (e.g., internet access) require high performance modulation, such as quadrature amplitude modulation (QAM), carrier amplitude and phase (CAP) modulation, or discrete multitone (DMT) modulation, while other applications (e.g., power monitoring and control) require only modest data rates and therefore a low performance modulation method. All users in the system will generally have to be equipped with a high performance modem to ensure modulation compatibility. These state of the art modems are then run at their lowest data rates for those applications that require relatively low data throughput performance. The replacement of inexpensive modems with much more expensive state of the art devices due to modulation compatibility imposes a substantial cost that is unnecessary in terms of the service and performance to be delivered to the end user.
Accordingly, what is sought, and what is not believed to be provided by the prior art, is a system and method of communication in which multiple modulation methods are used to facilitate communication among a plurality of modems in a network, which have heretofore been incompatible.
The present invention is generally directed to a system and method of communication between a master transceiver and a plurality of tributary transceivers in a multipoint communication system in which the tributary transceivers use different types of modulation methods. Broadly stated, the communication system includes a master transceiver in communication with a first tributary transceiver and a second tributary transceiver over a communication medium. The first tributary transceiver uses a primary modulation method for communication while the second tributary transceiver uses a secondary or embedded modulation method for communication. The master transceiver and tributary transceivers each include a processor, memory, and control logic for controlling their operation. While the primary modulation method is normally used for transmissions on the communication medium, the master transceiver can communicate with the second tributary transceiver by notifying the first tributary transceiver that the primary modulation method is being temporarily replaced by the secondary or embedded modulation method. The master transceiver can then exchange information with the second tributary transceiver while the first tributary transceiver ignores any secondary modulation transmissions. In the meantime, the first tributary transceiver conditions itself to look for a trailing sequence from the master transceiver indicating that communication with the second tributary transceiver is complete. When the master transceiver transmits the trailing sequence using the primary modulation method, the first tributary transceiver conditions itself to look for primary modulation transmissions while the second tributary transceiver conditions itself to ignore primary modulation transmissions.
The present invention has many advantages, a few of which are delineated hereafter as merely examples.
One advantage of the present invention is that it provides to the use of a plurality of modem modulation methods on the same communication medium.
Another advantage of the present invention is that a master transceiver can communicate seamlessly with tributary transceivers or modems using incompatible modulation methods.
Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention.